Vehicles often include an electronic key system that verifies an electronic key with an electronic key ID transmitted through wireless communication from the electronic key. In such an electronic key system, the electronic key needs to be registered to the vehicle. Thus, the electronic key or an encryption code is registered in advance to a controller such as an electronic control unit that manages the operation of the electronic key system in the vehicle. Japanese Laid-Open Patent Publication Nos. 7-61328, 2003-148018, and 2004-107959 each describe an example of an electronic key registration system.